An example of technologies that perform non-destructive inspection of the state of a welded portion and the state of a weld defect of a joined area between plate-like structures, an object to be inspected, is an ultrasonic test technology.
As an example of the ultrasonic inspection apparatuses employing the ultrasonic test technology, there is provided an ultrasonic inspection apparatus described in Japanese Unexamined Patent Application Publication Nos. 2003-149213 and 2004-53360.
In the ultrasonic inspection apparatus, an ultrasonic transducer, including a large number of piezoelectric vibrators disposed in a matrix, is used for production and detection of an ultrasonic wave. When a welded portion of an object to be inspected is subjected to imaging processing, the ultrasonic wave produced by the piezoelectric vibrators of the ultrasonic transducer is made incident on the welded portion, which is an joined area of the object to be inspected, a reflection echo of the ultrasonic wave reflected by the welded portion is received by the ultrasonic transducer, an electric signal corresponding to the received reflection echo is sent to a signal processing unit through a signal detecting circuit, and the echo signal is subjected to a parallel arithmetic processing in the signal processing unit. In the ultrasonic inspection apparatus, an ultrasonic image of the welded portion, subjected to image processing, is displayed on a display device so that, by means of visual inspection of the ultrasonic image, the states of the welded portion and a weld defect can be inspected without being destroyed.
In the known ultrasonic inspection apparatus, the states of a welded portion and a weld defect are inspected without being destroyed (in a non-destructive manner), by irradiating the welded portion of the object to be inspected with an ultrasonic wave, by performing imaging processing on the reflected echo to display an ultrasonic image on a display device, and by examining the displayed image of the welded portion by means of viewing.
Specifically, as described in Japanese Unexamined Patent Application Publication No. 11-326287, when a plate-like structure is the object to be inspected, and two plate-like structures are superposed and joined together by means of spot welding, by inspecting the states of the welded portion between the two plate-like structures and a weld defect using the ultrasonic inspection apparatus, in a non-destructive manner, it is possible to inspect whether a molten-solidified portion exists in the welded portion or not, and the presence or absence of the weld defect such as a blowhole, and the state of the weld defect.
Moreover, from Japanese Unexamined Patent Application Publication No. 6-265529, it is known that the bonding strength of the welded portion of the object to be inspected depends on the size of the molten-solidified portion, and the boundary between the joined area and the molten-solidified portion formed on the inner side thereof can be obtained from the inflexion point of the strength distribution curve of a reflection echo at the bottom portion of the joined area of the object to be inspected.
In the known ultrasonic inspection apparatus, a layer structure of an object to be inspected having a plurality of different acoustic properties, and defects, voids, and peelings of the welded portion of the object to be inspected can be visualized by means of an ultrasonic wave, and examined by viewing of the ultrasonic image of a welded portion displayed on the display device. However, since a two-dimensional ultrasonic image has been examined by means of viewing, fluctuations in the examination results has been occurred due to differences in opinion between individual examiners, and it has been difficult to quantitatively inspect the positional relationship of the welded portion with respect to the object to be inspected, correctly and accurately in three dimensions. In other words, the known ultrasonic inspection apparatus has the following problems.
1. Since internal inspection of the object to be inspected is performed by observing an ultrasonic image formed by imaging processing, it is difficult to inspect the states of the welded portion and the weld defect, objectively and quantitatively with high accuracy.
2. It has been difficult to automatically determine whether an abnormality has been present or not, quantitatively and accurately, from information representing the states of the welded portion and the weld defect displayed in the ultrasonic image obtained by performing imaging processing on the inside of the object to be inspected.
Moreover, in a more specific example, in the known ultrasonic inspection apparatus, as a sensing device for ultrasonic inspection (ultrasonic sensor), an ultrasonic transducer including piezoelectric elements disposed in a matrix or an array for emitting and receiving an ultrasonic wave is used, and the ultrasonic wave is made incident on the object to be inspected by fastening and fixing a shoe material, which is an acoustic wave propagating liquid medium, to the emitting and receiving surfaces of the ultrasonic sensor with bolts and by bringing the shoe material into close contact with the object to be inspected.
A portion of the ultrasonic wave entering the object to be inspected, is reflected by internal defects and interfaces of the object to be inspected to be the reflection echo, and three-dimensional imaging of the inside of the object to be inspected is performed by receiving the reflection echo by means of the ultrasonic sensor, vibrating each piezoelectric element of the ultrasonic sensor, and processing the generated electric signals.
Moreover, since the ultrasonic wave can not propagate when an air layer is present between the ultrasonic sensor and the object to be inspected, a couplant for acoustic matching of the ultrasonic wave, is applied or interposed between the ultrasonic sensor and the shoe material and between the shoe material and the object to be inspected. As the couplant, a gel liquid or solid having low volatility is used. Air bubbles tends to exist in the portion in which the couplant is applied or interposed due to a temperature difference etc., thereby, before inspection of the object is performed by the ultrasonic inspection apparatus, it is required to confirm whether air bubbles are present or not. When air bubbles are found, the shoe material is removed and the couplant is again applied on the shoe material.
In such an ultrasonic inspection apparatus, air bubbles have tended to enter between the ultrasonic sensor and the shoe material, thus, each time entry of air bubbles have occurred, it has been required to remove from the shoe material from the ultrasonic sensor by removing the bolts, and to re-apply the couplant on the shoe material.
Moreover, when unevenness has been present on the surface of the object to be inspected, it is difficult to bring the shoe material into close contact with the object to be inspected by filling the gap using only the couplant.
In the ultrasonic inspection apparatus, when air bubbles have been present between the ultrasonic sensor and the object to be inspected, and therefore a gap have existed between them, since, it is difficult for the ultrasonic wave emitted from the ultrasonic sensor to enter the object to be inspected smoothly, and to receive the reflection echo, the ultrasonic wave and the reflection echo are not correctly propagated, resulting in problems that detection performance degraded, and three-dimensional imaging processing of the inside of the object to be inspected cannot be performed correctly and smoothly.